feat(user): support fixed UUID registration and enhance bulk import results

- Added support for fixed UUIDs during bulk registration (Search-first + ExternalID mapping)
- Implemented idempotency and visibility restoration for soft-deleted users
- Enhanced bulk upload UI to show 'New/Updated/Unchanged' status and modified fields
- Added logic to reclaim identifiers (login_id) from colliding records
- Added frontend E2E and backend unit tests for UUID integrity and conflict handling
- Fixed i18n, formatting, and mock tests to satisfy code-check
- Applied 'go fix' for 'omitzero' tags and general Go standards

backend/internal/service/keto_service_test.go

@@ -36,7 +36,7 @@ func TestKetoService_CreateRelation(t *testing.T) {
 		assert.Equal(t, "/admin/relation-tuples", r.URL.Path)
 		assert.Equal(t, "PUT", r.Method)
 
-		var body map[string]interface{}
+		var body map[string]any
 		_ = json.NewDecoder(r.Body).Decode(&body)
 		assert.Equal(t, "tenants", body["namespace"])
 		assert.Equal(t, "tenant1", body["object"])